During earthquakes, large man made structures such as houses are frequently damaged and collapse as a result of the structural damage caused by the earthquake ground movement. People trapped in the fallen structures are often severely injured or killed. While many newer structures are built to withstand earthquakes up to a certain predicted magnitude, many other existing structures must be retrofitted with additional support to prevent failure in the event of a large earthquake.
An area of particular weakness is the garage door, which is typically a large rectangular opening in the wall of the garage structure. The door normally includes a frame that has two side posts and a horizontal member that spans the two posts. The space between the posts must provide enough space to drive one or more cars through. The door area is weak because of this large unsupported opening. In contrast, the walls of the garage may comprise closely spaced posts and beams or may even be solid materials such as poured concrete.
The garage door itself typically is positioned behind the door frame and is attached to an opening mechanism such as a track or beam actuator. During a large earthquake, the top of the door frame sways from side to side while the base is typically bound to the foundation and does not move. Because the door is behind the door frame, both will move independently during the earthquake and the door will not provide any structural support for the door frame.
The door frame is particularly vulnerable to the earthquake movement that is in line with the plane of the frame. As the ground moves below the garage, the posts of the door frame sway which causes stress at the upper corners of the door frame. If the corners of the frame are broken, the frame can easily collapse. Because of this inherent weakness, garage door frame need to be heavily reinforced to prevent failure during a strong earthquake. Unfortunately, many garage doors are not reinforced and are susceptible to failure during an earthquake. What is needed is a system that improves the strength of the garage door frame that can be retrofitted onto existing garage doors.